Calla is really not "out there"; its beautiful and has been around for a long time as a girl name.

But, if you'd like other names that mean lily or have ties to lilies, try some of these:Susan (there are lots of variations and spins on this one)ShoshanaNeejaRen
Clivia
CrinaZana
Asphodel
AzucenaLelia
Sonel
AnaliliaLeilaLilith
And of course the many variations of Lillian

You can also combine bits and pieces of other names with Lil or Calla, such as Callabeth or Roselily (Johnny Depp named his daughter Rose-Lily). This is only if you really think Calla or Lily just won't cut it by themselves. If you do this, choose wisely, and make sure it flows well (which may be tricky).